Comparison of observed and theoretical millimeter wave emission: implications for remote sensing of atmospheric water

Surface observations of atmospheric emission at 20, 31, and 90 GHz are compared with values predicted by theoretical models using radiosonde input data. Measurements are shown for continental locations in the United States, and shipboard- and island-based sites in the North Atlantic and tropical Pacific Oceans. Measurements are compared with commonly-used prediction models of Liebe. Differences between measurements and theory during clear conditions are shown to be caused largely by differences in the radiosonde humidity element. The impact of the observed discrepancies upon ground-based radiometric measurements of water vapor is discussed. A method to account for the differences and to reduce the water substance measurement error is presented.